A previous leak detection system employs a differential flow sensing principle for detecting fuel vapor leakage from the evaporative emission system of an automotive vehicle during a leakage test that involves closing the canister purge solenoid (CPS) valve and then positively pressurizing that portion of the evaporative emission system that is upstream of the CPS valve relative to the engine. One of the advantages of that leak detection system is that it less complicated than earlier known leak detection systems, and hence more economical and reliable, than prior known systems not using the differential flow sensing principle.
Another leak detection system utilizes a differential flow sensing principle, but does so in a way that is less influenced by certain variables, such as ambient temperature, pressure, engine manifold vacuum, or supply voltage.
Both of these leak detection systems utilize calibrated orifices, in conjunction with flow sensors and associated electronics as elements of the leak detectors.
The present invention is directed toward an on-board system for detecting fuel vapor leakage from an evaporative emission control system of an automotive vehicle.
Briefly, one aspect of the present invention relates to a novel organization and arrangement of a pressurizing pump, a single flowmeter, including associated electric signal processing for a signal obtained from the flowmeter, and a valve mechanism: that collectively allow an evaporative emission space to be quickly pressurized to appropriate test pressure at the beginning of a leak detection test, but will abort the test if conditions not conducive to obtaining an accurate result are discovered; that assure test accuracy by providing substantial insensitivity to extraneous disturbances during a test; that assure test accuracy by identification of test results obtained during conditions not conducive to attainment of an accurate result; that are well-suited for long-term reliability of test results by compensating for age-induced changes in the flowmeter characteristics; and that can be efficiently packaged into an assembly that is adapted for installation in a specific model of automotive vehicle by utilizing a specific adapter part for that model.
A preferred embodiment of the present invention comprises an electric-operated impeller pump for pressurizing the evaporative emission space under test, a cylindrical flow channel through which the impeller pump pressurizes the evaporative emission space under test, a single thermistor whose body is disposed in the flow channel to sense flow through the channel, electric signal processing associated with the thermistor for processing a signal obtained from the thermistor, and a valve mechanism which allows atmospheric air to be rapidly drawn into the impeller pump during pressurizing of the space under test, and which, once appropriate test pressure has been developed in the space under test, provides a restriction that is beneficial in rendering the leak detection test substantially insensitive to certain extraneous disturbances which otherwise might impair test accuracy.
Moreover, a specific presently preferred test procedure employs an algorithm that initially performs a "pinched-line" test, and upon its successful passage, a leak detection test. It also performs a self-test of the thermistor and associated signal processing so that any drift in the thermistor characteristics is noted and automatically compensated for.
A preferred practice which is disclosed hereinafter for pressurizing the evaporative emission space under test comprises conducting the pressurizing airflow into the space via the vapor collection canister's (charcoal canister's) atmospheric vent port to create a superatmospheric pressure for use in leak detection. Because the impeller pump provides an open passage through itself when not being operated, the association of an assembly embodying the present invention with an evaporative emission space allows the pumped air flow to be communicated to the canister vent port without adversely affecting atmospheric venting of the evaporative emission space through the canister vent port during times of non-testing.
The compactness of a leak detection pump and flowmeter assembly which embodies principles of the present invention can provide spatial economy that may be especially important to many automobile manufacturers. A unitary leak detection pump and flowmeter assembly also has the advantage of requiring fewer connections of components in an automotive assembly plant, and this affords an opportunity for installation cost savings while at the same time an opportunity for increased reliability of installation. A unitary leak detection pump and assembly may be integrated with a canister, or remotely located and communicated to the vapor confinement space by a conduit.
The generic principles of the invention extend however to embodiments that are non-unitary, that is to embodiments where, for example, a pump may be remotely located from a leak detection assembly and/or a leak detection assembly may be located remotely from a canister. In the design of certain vehicles, the ability to locate various components in various locations may be important for packaging purposes. Suitable conduits communicate the remotely located components.
The inventive leak detection pump and flowmeter assembly possesses significant economies of scale in its manufacture because all major component parts can be commonly mass-produced and assembled with only a special adapter part being required for adapting the assembly to a particular vehicle model.
Accordingly, in one general respect, the invention relates to a leak detection system for detecting leakage from a portion of a vapor confinement space which is upstream of an inlet of a canister purge valve relative to an engine and comprises: a pump for pumping a gaseous medium; a flowpath providing communication between the pump and the vapor confinement space; a flowmeter for measuring flow of gaseous medium through the flowpath; the flowmeter comprising an electric circuit element disposed in the flowpath to be exposed to flow of gaseous medium through the flowpath; the electric circuit element having a predetermined temperature vs. electric current characteristic that enables the electric circuit element to provide a signal correlated to flow of gaseous medium through the flowpath; and an electric circuit to which the electric circuit element is operatively connected for supplying electric current to the electric circuit element and for creating a signal representative of electric current flow through the electric circuit element, and hence of flow of gaseous medium through the flowpath.
In another general respect, the invention relates to a leak detection system for detecting leakage from a portion of a vapor confinement space which is upstream of an inlet of a canister purge valve relative to an engine and comprises: a pump for pumping a gaseous medium; a flowpath providing communication between the pump and the vapor confinement space; a flowmeter for measuring flow of gaseous medium through the flowpath; and in which the pump comprises an outlet communicated via the flowpath to the vapor confinement space and an inlet that is selectively communicated to atmosphere via a valve, means causing the valve to be open while the pump operates to pressurize the vapor confinement space to a predetermined superatmospheric pressure, and means causing the valve to be closed when the pressure in the vapor confinement space is at the predetermined superatmospheric pressure.
In still another general respect, the invention relates to an assembly for use in a leak detection system operatively associated with the evaporative emission control system of an engine powered automotive vehicle for detecting leakage from a portion of a vapor confinement space which is upstream of an inlet of a canister purge valve relative to an engine, wherein the assembly comprises: a housing comprising a first port adapted to be communicated to a pump, a second port adapted to be communicated to a vapor confinement space, and two parallel branches in that portion of the flowpath that passes through the housing; a flowmeter for measuring flow of gaseous medium through the flowpath; and a valve for allowing and disallowing flow through one of the two branches.
In a still further general respect, the invention relates to a leak detection system for detecting leakage from a portion of a vapor confinement space which is upstream of an inlet of a canister purge valve relative to an engine and comprises: a pump for pumping a gaseous medium; a flowpath providing communication between the pump and the vapor confinement space; a flowmeter for measuring flow of gaseous medium through the flowpath; an electric circuit for selectively operating the pump and for processing the gaseous flow measurement of the flowmeter in accordance with an algorithm that comprises means for causing the electric circuit to detect a first state of stability of the gaseous flow measurement of the flowmeter while the pump is running, means for causing the electric circuit to detect a second state of stability of the gaseous flow measurement of the flowmeter while the pump is not running, and means for causing the electric circuit to process the value of the first state of stability of the gaseous flow measurement of the flowmeter and the value of the second state of stability of the gaseous flow measurement of the flowmeter.
In a still further general respect, the invention relates to a leak detection system for detecting leakage from a portion of a vapor confinement space which is upstream of an inlet of a canister purge valve relative to an engine and comprises: pumping a gaseous medium through a flowpath that communicates the vapor confinement space to atmosphere; measuring flow of gaseous medium through the flowpath; selectively operating the pump and processing the gaseous flow measurement of the flowmeter in accordance with an algorithm that detects a first state of stability of the gaseous flow measurement of the flowmeter while the pump is running, that detects a second state of stability of the gaseous flow measurement of the flowmeter while the pump is not running, and processing the value of the first state of stability of the gaseous flow measurement of the flowmeter and the value of the second state of stability of the gaseous flow measurement of the flowmeter.
The foregoing, along with further features, advantages, and benefits of the invention, will be seen in the ensuing description and claims, which are accompanied by drawings. The drawings, which are incorporated herein and constitute part of this specification, illustrate the presently preferred embodiments of the invention according to the best mode contemplated at this time for carrying out the invention.